In a typical cloud data center environment, there is a large collection of interconnected servers that provide computing and/or storage capacity to run various applications. For example, a data center may comprise a facility that hosts applications and services for subscribers, i.e., customers of data center. The data center may, for example, host all of the infrastructure equipment, such as networking and storage systems, redundant power supplies, and environmental controls. In a typical data center, clusters of storage systems and application servers are interconnected via high-speed switch fabric provided by one or more tiers of physical network switches and routers. More sophisticated data centers provide infrastructure spread throughout the world with subscriber support equipment located in various physical hosting facilities.
Network virtualization, whereby hardware and software network resources are combined into a single, software-based administrative entity, is commonly used today. Typical network architecture may include a plurality of chassis connected to virtual network servers via a plurality of Top-of-the-Rack (TOR) switches. Each virtual network server includes a plurality of virtual machines in virtual subnets. The virtual network usually includes an overlay network, in which nodes are connected by virtual links, and an agent that controls the overlay network.
In a physical network, when a connection between a TOR and a server fails, a message will not be delivered to the server as intended. If the virtual network controller becomes aware of the failure, it can reroute the message via an alternate route. However, unless the virtual network controller becomes aware of the failed link and reroutes the message, messages will not reach the intended destination. In a virtualized network environment, this problem can in some cases be addressed for virtual machines by using overlay networks and encapsulation. However, encapsulation adjustment may not be possible for Agents at the servers, which control the overlay. In the worst case, the Agent and the virtual network controller may lose connection with each other.